A proposed breeding program for the critically endangered Siamese crocodile received a significant boost this month with the news that 35 crocodiles at a wildlife rescue center in Cambodia are purebred Siamese.

A proposed breeding program for the critically endangered Siamese crocodile received a significant boost this month with the news that 35 crocodiles at a wildlife rescue center in Cambodia are purebred Siamese.

Siamese crocodiles have had a tough time. Twenty years ago they were declared extinct in the wild.

The crocodiles once ranged widely across Southeast Asia. But, coveted for their soft skin, Siamese crocodiles were poached to the very edge of existence.

However, in 2001 researchers discovered small populations of Siamese crocodiles in the wild in Cambodia. That meant the species went from being listed as extinct to critically endangered.

This month there was more good news. DNA tests on 69 crocodiles at a wildlife rescue center outside Phnom Penh found that 35 of them are purebred Siamese crocodiles.

Adam Scott, head of the crocodile project at Fauna and Flora International, holding a hatchling Siamese crocodile at Phnom Tamao Wildlife Rescue Centre

Adam Starr heads the crocodile conservation program at Fauna and Flora International, a conservation organization that works with the Cambodian government to protect Siamese crocodiles.

He says just 250 Siamese crocodiles exist in the wild in the world, most of them in Cambodia.

"How important is Cambodia? Very important. Siamese crocodiles used to exist throughout Southeast Asia. Indonesia, Malaysia, Thailand, Cambodia, Laos, Vietnam, everywhere. Now they are reduced from about 99 percent of their original population range area. We can say Cambodia hosts between 95 and 99 percent of the remaining wild crocodiles which is about 250," he said.

The tests proved invaluable in allowing researchers to distinguish between purebred Siamese crocodiles and hybrid crocodiles - something that can not be done just by looking at them.

Knowing which animals are hybrid is essential because conservationists do not want hybrids colonizing the country's rivers.

Nhek Ratanapech is the director of the Phnom Tamao Wildlife Rescue Center, where the purebred crocodiles live. He also heads the country's Crocodile Conservation Program.

He says the discovery of the purebreds could provide a critical lifeline for the preservation of Siamese crocodiles.

"Previously we have so many crocodiles but we didn't know which ones are pure Siamese crocodiles and which one is the hybrid one," he said. "Now we know exactly which one is pure and which is hybrid. We do hope that some potential donor help to support the activity to conserve or to stop this species being extinct from the world."

The problem of hybrids stems from crocodile farms, which bred Siamese crocodiles with other, faster-growing, larger, more aggressive crocodiles. The leather from the hybrid crocodile is still soft, and the hybrids provide more of it faster.

Nhek Ratanapech says the next step is to create a breeding program using the six mature purebreds at his center. The tests also showed that they are not related, which is vital for genetic diversity.

Their offspring will be kept for two years before being released into the wild, to maximize their chances of survival.

Nhek Ratanapech says the goal is to get Siamese crocodiles taken off the critically endangered list, which means reaching a target of 500 mature adults in the wild. As it takes 15 years for a Siamese crocodile to reach maturity, this is a long-term project.

But Cambodia is the Siamese crocodile's last chance. "So this population is on the verge of extinction and now Cambodia is the stronghold of this species," he said.

Adam Starr says many challenges remain. Human encroachment on the crocodile habitat is one problem; another is Cambodia's plans to build huge hydroelectric dams, which block rivers.

But those challenges are hardly new. And the DNA tests, which were carried out by a university in Thailand, have helped to move the project forward.

"What we're able to do now is work with a captive population that is of pure genetic stock and be able to start a breeding program and be able to reintroduce animals to areas where Siamese crocodiles once existed but have been eradicated due to poaching. So it's a very exciting phase we're about to embark upon," said Starr.

That sound is the call of a Siamese crocodile hatchling. It is a sound that Nhek Ratanapech and his colleagues hope will be heard across at least some of Cambodia's rivers in the coming years - as it was not long ago.